Deuteron Spin Structure Functions Research Articles

Impact of recent COMPASS data on polarized parton distributions and structure functions

We perform a new extraction of polarized parton distribution functions (PPDFs) from the spin structure function experimental data in the fixed-flavor number scheme (FFNS). In this analysis, we include recent proton and deuteron spin structure functions obtained by the \texttt{COMPASS} collaboration. We examine the impact of the \texttt{new COMPASS} proton and deuteron data on the polarized parton densities and compare with results from our previous study (KATAO PPDFs), which used the Jacobi polynomial approach. We find the extracted PPDFs of the proton, neutron, and deuteron structure functions are in very good agreement with the experimental data. The results for extracted PPDFs are also compared with available theoretical models from the literature.

Measurement of the Q^{2} Dependence of the Deuteron Spin Structure Function g_{1} and its Moments at Low Q^{2} with CLAS.

We measured the g_{1} spin structure function of the deuteron at low Q^{2}, where QCD can be approximated with chiral perturbation theory (χPT). The data cover the resonance region, up to an invariant mass of W≈1.9 GeV. The generalized Gerasimov-Drell-Hearn sum, the moment Γ_{1}^{d} and the spin polarizability γ_{0}^{d} are precisely determined down to a minimum Q^{2} of 0.02 GeV^{2} for the first time, about 2.5 times lower than that of previous data. We compare them to several χPT calculations and models. These results are the first in a program of benchmark measurements of polarization observables in the χPT domain.

Precise determination of the deuteron spin structure at low to moderateQ2with CLAS and extraction of the neutron contribution

We present the final results for the deuteron spin structure functions obtained from the full data set collected with Jefferson Lab's CLAS in 2000-2001. Polarized electrons with energies of 1.6, 2.5, 4.2 and 5.8 GeV were scattered from deuteron ($^{15}$ND$_3$) targets, dynamically polarized along the beam direction, and detected with CLAS. From the measured double spin asymmetry, the virtual photon absorption asymmetry $A_1^d$ and the polarized structure function $g_1^d$ were extracted over a wide kinematic range (0.05 GeV$^2 < Q^2 <$ 5 GeV$^2$ and 0.9 GeV $< W <$ 3 GeV). We use an unfolding procedure and a parametrization of the corresponding proton results to extract from these data the polarized structure functions $A_1^n$ and $g_1^n$ of the (bound) neutron, which are so far unknown in the resonance region, $W < 2$ GeV. We compare our final results, including several moments of the deuteron and neutron spin structure functions, with various theoretical models and expectations as well as parametrizations of the world data. The unprecedented precision and dense kinematic coverage of these data can aid in future extractions of polarized parton distributions, tests of perturbative QCD predictions for the quark polarization at large $x$, a better understanding of quark-hadron duality, and more precise values for higher-twist matrix elements in the framework of the Operator Product Expansion.

New analysis concerning the strange quark polarization puzzle

The fact that analyses of semi-inclusive deep inelastic scattering suggest that the polarized strange quark density $\mathrm{\ensuremath{\Delta}}s(x)+\mathrm{\ensuremath{\Delta}}\overline{s}(x)$ is positive in the measured region of Bjorken $x$, whereas all analyses of inclusive deep inelastic scattering yield significantly negative values of this quantity, is known as the ``strange quark polarization puzzle.'' We have analyzed the world data on inclusive deep inelastic scattering, including the COMPASS 2010 proton data on the spin asymmetries, and for the first time, the new extremely precise JLab CLAS data on the proton and deuteron spin structure functions. Despite allowing, in our parametrization, for a possible sign change, our results confirm that the inclusive data yield significantly negative values for the polarized strange quark density.

1- Results from the SMC experiment at CERN. 2- The COMPASS experiment at CERN

SMC : The SMC collaboration has measured the proton and deuteron spin structure function g 1 in the kinematical range 0.00006 < x < 0.8 and 0.02 < Q 2 < 100 GeV 2. A brief summary of the NLO pQCD global analysis of all g 1 world data available in 1998 is given. The first moments of the proton, deuteron and neutron structure function were calculated in two factorization schemes ( MS and AB). They lead to a value of a 0 close to 0.2, which corresponds to ΔΣ= 0.19 in the MS scheme, and 0.38 in the AB one. The Bjorken sum rule is tested and found to agree with the theoretical predictions at the level of 10 %. COMPASS : The first goal of the COMPASS experiment at CERN is the measurement of the contribution of the gluon polarization Δ g to the nucleon spin. The measurement will be done by scattering high energy polarized muons on a polarized proton or deuteron target. The photon gluon fusion process, which is sensitive to the gluon density distribution, will be signed by the presence of charmed particles ( D 0, D 0) or of high p t hadrons pairs of opposite charge. In addition to Δ g, the longitudinal and transversely polarized parton distributions will be measured for the different flavors. A new spectrometer with large acceptance, high rate capability and identification of particles is being commissioned.

Nuclear shadowing in polarized deep inelastic scattering on6LiDat smallxand its effect on the extraction of the deuteron spin structure functiong1d(x,Q2)

We consider the effect of nuclear shadowing in polarized deep inelastic scattering (DIS) on ^6LiD at small Bjorken x and its relevance to the extraction of the deuteron spin structure function g_{1}^{d}(x,Q^2). Using models, which describe nuclear shadowing in unpolarized DIS, we demonstrate that the nuclear shadowing correction to g_{1}^{d}(x,Q^2) is significant.

Measurement of the deuteron spin structure function g1d( x) for 1 (GeV/c) 2< Q2

New measurements are reported on the deuteron spin structure function g 1 d . These results were obtained from deep inelastic scattering of 48.3 GeV electrons on polarized deuterons in the kinematic range 0.01< x<0.9 and 1< Q 2<40 (GeV/c) 2. These are the first high dose electron scattering data obtained using lithium deuteride ( 6 Li 2 H) as the target material. Extrapolations of the data were performed to obtain moments of g 1 d , including Γ 1 d , and the net quark polarization ΔΣ.

The Nucleon Axial Isoscalar Coupling and First Moments of p, n, d Spin Structure Functions11The project supported by National Natural Science Foundation of China

The nucleon coupling constant to the axial isoscalar current, , is calculated in the framework of QCD sum rules by including the effects of the three-gluon condensates. The contribution from the polarized strange sea quarks to is extracted in a constituent quark model with a QCD modification. The combined resultant theoretical value, , agrees with the experimental estimate. The first moments of the proton, neutron and deuteron spin structure functions are evaluated and compared with the experimental data.

Proton spin structure functions and generalized Sullivan processes.

We employ the time-ordered perturbation field theory in the infinite momentum limit, as developed extensively by Drell, Levy, and Yan, to derive the convolution formulas for the proton spin structure functions ${g}_{1}(x,{Q}^{2})$ and ${g}_{2}(x,{Q}^{2})$ suitable for the generalized Sullivan processes, in which the meson in the cloud or the recoiling baryon is struck and smashed by the virtual photon. Following a previous suggestion that the sea quark distributions of a nucleon at low and moderate ${Q}^{2}$ may be attributed primarily to such Sullivan processes, we use the convolution formulas to obtain the first moments ${\ensuremath{\Gamma}}_{p}\ensuremath{\equiv}\ensuremath{\int}{0}^{1}{g}_{1}^{p}(x,{Q}^{2})dx$ and ${\ensuremath{\Gamma}}_{n}\ensuremath{\equiv}\ensuremath{\int}{0}^{1}{g}_{1}^{n}(x,{Q}^{2})dx$, as well as to investigate ${g}_{1}^{p}(x,{Q}^{2})$ and ${g}_{1}^{n}(x,{Q}^{2})$ as a function of $x$. Our results indicate that both the data on ${g}_{1}^{p}(x,{Q}^{2})$ obtained previously by the European Muon Collaboration and the recent data on the deuteron spin structure function ${g}_{1}^{d}(x,{Q}^{2})$ obtained by the Spin Muon Collaboration can be understood and the Bjorken sum rule is satisfied. A comparison between our prediction on ${g}_{1}^{n}(x,{Q}^{2})$ and the recent SLAC data is also given.